Understanding the map function

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map(function, iterable, ...)

Apply function to every item of iterable and return a list of the results. If additional iterable arguments are passed, function must take that many arguments and is applied to the items from all iterables in parallel.

If one iterable is shorter than another it is assumed to be extended with None items.

If function is None, the identity function is assumed; if there are multiple arguments, map() returns a list consisting of tuples containing the corresponding items from all iterables (a kind of transpose operation).

The iterable arguments may be a sequence or any iterable object; the result is always a list.

What role does this play in making a Cartesian product?

content = map(tuple, array)

What effect does putting a tuple anywhere in there have? I also noticed that without the map function the output is abc and with it, it"s a, b, c.

I want to fully understand this function. The reference definitions is also hard to understand. Too much fancy fluff.

👻 Read also: what is the best laptop for engineering students?

Understanding the map function cartesian product: Questions

Get the cartesian product of a series of lists?

1 answers

û…u By û…u

How can I get the Cartesian product (every possible combination of values) from a group of lists?

Input:

somelists = [
   [1, 2, 3],
   ["a", "b"],
   [4, 5]
]

Desired output:

[(1, "a", 4), (1, "a", 5), (1, "b", 4), (1, "b", 5), (2, "a", 4), (2, "a", 5) ...]
399

Answer #1

itertools.product

Available from Python 2.6.

import itertools

somelists = [
   [1, 2, 3],
   ["a", "b"],
   [4, 5]
]
for element in itertools.product(*somelists):
    print(element)

Which is the same as,

for element in itertools.product([1, 2, 3], ["a", "b"], [4, 5]):
    print(element)

We hope this article has helped you to resolve the problem. Apart from Understanding the map function, check other cartesian product-related topics.

Want to excel in Python? See our review of the best Python online courses 2022. If you are interested in Data Science, check also how to learn programming in R.

By the way, this material is also available in other languages:



Anna OConnell

New York | 2022-12-03

Maybe there are another answers? What Understanding the map function exactly means?. Will get back tomorrow with feedback

Carlo Innsbruck

Massachussetts | 2022-12-03

cartesian product is always a bit confusing 😭 Understanding the map function is not the only problem I encountered. Checked yesterday, it works!

Angelo Krasiko

California | 2022-12-03

I was preparing for my coding interview, thanks for clarifying this - Understanding the map function in Python is not the simplest one. I am just not quite sure it is the best method

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